March 07, 2025 -- Scientists at Yokohama National University (YNU), in collaboration with RIKEN and other institutions in Japan and Korea, have developed a novel method to control electron distribution in molecules using ultrafast terahertz pulses.

This technique enables precise manipulation of electrons, allowing the addition or removal of charges from individual molecules, which can create excitons—energy packets that emit light. The research, published in Science on March 7, 2025, demonstrates how terahertz light can guide molecular processes at ultrafast timescales, potentially advancing applications in electronics, energy transfer, and chemical reactions.

Atoms and molecules contain negatively charged electrons that usually stay in specific energy levels, like layers, around the positively charged nucleus. How these electrons are arranged in the molecule is key to how the molecule behaves. This arrangement affects critical processes like how light is emitted, how charges move between molecules, and how chemical reactions happen.

For example, when light hits an electron and gives it enough energy, the electron moves to a higher energy level, leaving behind a positively charged “hole.” This creates an exciton—a tiny energy packet in the molecule that can emit light. This process is key to solar cells, where excitons help convert sunlight into electricity, and LEDs release energy as light.

The research at Yokohama National University involves the use of terahertz pulses to manipulate electron behavior in molecules. These ultrafast pulses enable precise control over electron transfer between a molecule and a metal tip, facilitating the creation or removal of electrons and forming excitons—energy packets that emit light when released. This method allows for the induction of charged states in molecules through mechanisms not achievable with conventional methods, potentially enhancing the efficiency of devices like solar cells and LEDs by improving charge transfer processes.

The application of terahertz pulses provides a novel approach to ultrafast electron control, offering insights into dynamic molecular processes. This technique is significant for nanotechnology and materials science, as it could lead to the design of new materials with tailored electronic properties. Additionally, it enables the study of chemical reactions and energy transfer at the molecular level, potentially advancing fields such as catalysis and energy storage.

“While excitons typically form when light is absorbed by a material, our findings reveal they can also be created through charged states using these specially designed terahertz pulses,” says Professor Ikufumi Katayama, the study’s corresponding author from the Faculty of Engineering at YOKOHAMA National University. “This opens new possibilities for controlling how charge moves within molecules, which could lead to better solar cells, smaller light-based devices, and faster electronics.”

Despite challenges in generating and controlling terahertz pulses and ensuring precise interaction without unintended effects, this technique represents a promising advancement in ultrafast electron control, opening new research and technological innovation possibilities.